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RF MEASUREMENT CHART

• The first three columns are conversion tables for return loss, reflection

coefficient, and SWR.

• The last four columns are values for inter actions of a small phasor X with a

large phasor (unity reference) expressed in dB related to reference.

The RF Measurement Chart can be used to determine the uncertainty due

to bridge/autotester VNA directivity. The “X dB Below Reference” column

represents the difference between the directivity and the measured

reflection (return loss). The “ref + X dB” and “ref – X dB” values are the

algebraic sum of the error signal and the measured reflected signal as their

phase relationship varies over 360˚. Therefore, the peak-to-peak ripple

(1 ± X) is the total measurement uncertainty caused by the error signal.

For example, if a 30 dB return loss is measured with a 40 dB directivity auto

tester, the X dB Below Reference value is 10 dB. Ref + X dB is 2.3866 dB and

ref – X dB is 3.3018 dB. The actual return loss is between 27.6134 dB (– 30 +

2.3866) and 33.3018 dB (– 30 – 3.3018). The peak to peak ripple on a swept

measurement will be 5.6884 dB. If the error and directivity signals are equal,

ref +X dB equals 6 dB (voltage doubled causes 6 dB change) and ref – X dB

becomes infinite, , since the two signals are equal in amplitude and 180∞ out

of phase (zero voltage).

(Ref+X)

(Ref-X)

(Ref)

Phasor Interaction

Above ANSI Standard tolerance applies to all components unless otherwise noted.

ANSI Standard

X mm

±5 mm

X.X mm

±0.5 mm

X.XX mm

±0.15 mm

X.XXX mm

±0.05 mm

Relative to Unity Reference

SWR Reflection Coefficient Return Loss (dB) X dB Below Reference Ref +X (dB) Ref –X (dB) Ref ±X (dB)

17.3910 0.8913 1 1 5.5350 19.2715 24.8065

8.7242 0.7943 2 2 5.0780 13.7365 18.8145

5.8480 0.7079 3 3 4.6495 10.6907 15.3402

4.4194 0.6310 4 4 4.2489 8.6585 12.9073

3 5698 0.5623 5 5 3.8755 7.1773 11.0528

3.0095 0.5012 6 6 3.5287 6.0412 9.5699

2.6146 0.4467 7 7 3.2075 5.1405 8.3480

2.3229 0.3981 8 8 2.9108 4.4096 7.3204

2.0999 0.3548 9 9 2.6376 3.8063 6.4439

1.9250 0.3162 10 10 2.3866 3.3018 5.6884

1.7849 0.2818 11 11 2.1567 2.8756 5.0322

1.6709 0.2512 12 12 1.9465 2.5126 4.4590

1.5769 0.2239 13 13 1.7547 2.2013 3.9561

1.4985 0.1995 14 14 1.5802 1.9331 3.5133

1.4326 0.1778 15 15 1.4216 1.7007 3.1224

1.3767 0.1585 16 16 1.2778 1.4988 2.7766

1.3290 0.1413 17 17 1.1476 1.3227 2.4703

1.2880 0.1259 18 18 1.0299 1.1687 2.1986

1.2528 0.1122 19 19 0.9237 1.0337 1.9574

1.2222 0.1000 20 20 0.8279 0.9151 1.7430

1.1957 0.0891 21 21 0.7416 0.8108 1.5524

1.1726 0.0794 22 22 0.6639 0.7189 1.3828

1.1524 0.0708 23 23 0.5941 0.6378 1.2319

1.1347 0.0631 24 24 0.5314 0.5661 1.0975

1.1192 0.0562 25 25 0.4752 0.5027 0.9779

1.1055 0.0501 26 26 0.4248 0.4466 0.8714

1.0935 0.0447 27 27 0.3798 0.3969 0.7765

1.0829 0.0398 28 28 0.3391 0.3529 0.6919

1.0736 0.0355 29 29 0.3028 0.3138 0.6166

1.0653 0.0316 30 30 0.2704 0.2791 0.5495

1.0580 0.0282 31 31 0.2414 0.2483 0.4897

1.0515 0.0251 32 32 0.2155 0.2210 0.4365

1.0458 0.0224 33 33 0.1923 0.1967 0.3890

1.0407 0.0200 34 34 0.1716 0.1751 0.3467

1.0362 0.0178 35 35 0.1531 0.1558 0.3090

1.0322 0.0158 36 36 0.1366 0.1388 0.2753

1.0287 0.0141 37 37 0.1218 0.1236 0.2454

1.0255 0.0126 38 38 0.1087 0.1100 0.2187

1.0227 0.0112 39 39 0.0969 0.0980 0.1949

1.0202 0.0100 40 40 0.0864 0.0873 0.1737

1.0180 0.0089 41 41 0.0771 0.0778 0.1548

1.0160 0.0079 42 42 0.0687 0.0693 0.1380

1.0143 0.0071 43 43 0.0613 0.0617 0.1230

1.0127 0.0063 44 44 0.0546 0.0550 0.1096

1.0113 0.0056 45 45 0.0487 0.0490 0.0977

1.0101 0.0050 46 46 0.0434 0.0436 0.0871

1.0090 0.0045 47 47 0.0387 0.0389 0.0776

1.0080 0.0040 48 48 0.0345 0.0346 0.0692

1.0071 0.0035 49 49 0.0308 0.0309 0.0616

1.0063 0.0032 50 50 0.0274 0.0275 0.0549

1.0057 0.0028 51 51 0.0244 0.0245 0.0490

1.0050 0.0025 52 52 0.0218 0.0218 0.0436

1.0045 0.0022 53 53 0.0194 0.0195 0.0389

1.0040 0.0020 54 54 0.0173 0.0173 0.0347

1.0036 0.0018 55 55 0.0154 0.0155 0.0309

1.0032 0.0016 56 56 0.0138 0.0138 0.0275

1.0028 0.0014 57 57 0.0123 0.0123 0.0245

1.0025 0.0013 58 58 0.0109 0.0109 0.0219

1.0022 0.0011 59 59 0.0097 0.0098 0.0195

1.0020 0.0010 60 60 0.0087 0.0087 0.0174